Expandable interbody fusion cage

ABSTRACT

An expandable intervertebral device including a body extending generally along a longitudinal axis and including at least two branch portions coupled together adjacent an end portion of the body. The device further includes an expansion member positioned between the at least two branch portions with at least a portion of the expansion member arranged at an angular orientation relative to the longitudinal axis whereby a change in the angular orientation relative to the longitudinal axis urges the at least two branch portions apart to expand the body.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.09/949,516, filed Sep. 7, 2001, now abandoned, which is a continuationof U.S. application Ser. No. 09/763,073, filed May 16, 2001 and issuedas U.S. Pat. No. 6,436,140, which claims foreign priority benefits ofInternational Patent Application Number PCT/1B99/01478, filed Aug. 26,1999, and French Patent Application Number FR98/10832, filed on Aug. 28,1998, the contents of each application hereby being incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to an implantable device for promotingfusion between two adjacent bony structures and a method of insertingthe same. More particularly, the invention relates to an expandablefusion cage that may be inserted, in a reduced size configuration, intoan intervertebral space and expanded after insertion to provide adesired size. While the device according to the present invention mayhave application in other areas of the body, the present invention ispreferably utilized for vertebral interbody fusion.

There have been an extensive number of attempts to develop anexceptional intradiscal implant that could be used to replace a damageddisc and yet maintain the stability of the disc interspace betweenadjacent vertebra, at least until complete arthrodesis is achieved.These “interbody fusion devices” have taken many forms. For example, oneof the more prevalent designs takes the form of a cylindrical implant.These types of implants are presented by the patents to Bagby, U.S. Pat.No. 4,501,269; Brantigan, U.S. Pat. No. 4,878,915; Ray, U.S. Pat. Nos.4,961,740 and 5,055,104; and Michelson, U.S. Pat. No. 5,015,247. In thecylindrical implants, the exterior portion of the cylinder can bethreaded to facilitate insertion of the interbody fusion device, asrepresented by the Ray, Brantigan and Michelson patents. In thealternative, some of the fusion implants are designed to be pounded intothe intradiscal space. This type of device is represented by the patentto Brantigan.

Interbody fusion devices can be generally divided into two basiccategories, namely solid implants and implants that are designed topermit bone in-growth. Solid implants are represented by U.S. Pat. Nos.4,879,915; 4,743,256; 4,349,921; and 4,714,469. The remaining patentsdiscussed above include some aspect that allows bone to grow across theimplant. It has been found that the devices that promote natural bonein-growth achieve a more rapid and stable arthrodesis. The devicedepicted in the Michelson patent is representative of this type ofhollow implant which is typically filled with a bone growth inducingsubstance to promote bone growth into and through the device. Thisimplant includes a plurality of circular apertures which communicatewith the hollow interior of the implant, thereby providing a path fortissue growth between the vertebral end plates and the bone growthmaterial within the implant. In preparing the intradiscal space, the endplates are preferably reduced to bleeding bone to facilitate the tissuein-growth. During fusion, the metal structure provided by the Michelsonimplant helps maintain the patency and stability of the motion segmentto be fused. In addition, once arthrodesis occurs, the implant itselfserves as a sort of anchor for the solid bony mass.

One problem that is not addressed by the above prior devices concernsmaintaining and restoring the normal anatomy of the fused spinalsegment. Naturally, once the disc is removed, the normal lordotic orkyphotic curvature of the spine is eliminated. With the prior devices,the need to restore this curvature is neglected. For example, adjacentvertebral bodies may be reamed with a cylindrical reamer that fits theparticularly implant. In some cases, the normal curvature is establishedprior to reaming and then the implant inserted. However, thisover-reaming of the posterior portion is generally not well acceptedbecause of the removal of load bearing bone of the vertebrae and becauseit is typically difficult to ream through the posterior portion of thelower lumbar segment where the lordosis is the greatest. In most casesusing implants of this type, no effort is made to restore the lordoticcurvature so that the cylindrical implant is likely to cause a kyphoticdeformity as the vertebrae settles around the implant. This phenomenacan often lead to revision surgeries because the spine becomesimbalanced.

In each of the above-listed patents, the transverse cross-section of theimplant is substantially constant throughout its length and is typicallyin the form of a right circular cylinder. Other implants have beendeveloped for interbody fusion that do not have a constantcross-section. For instance, the patent to McKenna, U.S. Pat. No.4,714,469 shows a hemispherical implant with elongated protruberancesthat project into the vertebral end plate. Further, U.S. Pat. No.5,669,909 to Zdeblick et al., shows a truncated conical implant adaptedto be threadedly received in the intervertebral space. However, thesedevices require an opening at least as large as the largest segment ofthe device. The requirement for such a relatively large opening maylimit the use of such devices, particularly where access to the spine islimited due to obstructing vessels and neurological structures.

Still further implants have been developed that provide the ability toadjust the size of the implant after insertion. U.S. Pat. Nos. 5,665,122to Kambin, 5,554,191 to LaHille et al., and 5,653,763 to Errico et al.disclose implants which provide at least some degree of adjustability ofthe height of the implant to restore lordosis. However, these implantsdo not allow the device to be easily and securely inserted into a discspace and the internal expansion mechanism limits the ability to packthe interior with a large amount of bone in-growth material.

In view of the limitations of the prior devices, there remains a needfor an expandable interbody device capable of stabilizing the spine in amanner comparable to interbody implant designs presently in use, and atthe same time providing a mechanism for restoring normal lordosis of thespine. After expansion, the device should have an internal cavityadapted to receive bone graft or bone substitute to encourage bonegrowth through the expanded device.

SUMMARY OF THE INVENTION

In response to the needs still left unresolved by the prior devices, thepresent invention contemplates an expandable intervertebral deviceadapted to be inserted between a pair of vertebral bodies to restore thenormal angular relation between adjacent vertebrae. In particular, anexpandable intervertebral device according to one form of the presentinvention includes a body extending generally along a longitudinal axisand including at least two branch portions coupled together adjacent anend portion of the body. The device further includes an expansion memberpositioned between the at least two branch portions with at least aportion of the expansion member arranged at an angular orientationrelative to the longitudinal axis whereby a change in the angularorientation relative to the longitudinal axis urges the at least twobranch portions apart to expand the body.

In another form of the present invention, an expandable intervertebraldevice is provided including a body extending generally along alongitudinal axis and including at least two branch portions coupledtogether adjacent an end portion of the body, with the body defining aseries of ratchet elements positioned along the longitudinal axis. Thedevice further includes an expansion member positioned between the atleast two branch portions whereby axial movement of the expansion membergenerally along the longitudinal axis urges the at least two branchportions apart to expand the body with a portion of the expansion memberengaged with at least one of the ratchet elements to maintain theexpansion member in a select axial position along the longitudinal axisrelative to the body.

In another form of the present invention, an expandable intervertebraldevice is provided including a body extending generally along alongitudinal axis and having a fixed end portion and a movable endportion, with the body including at least two branch portions coupledtogether adjacent the fixed end portion. The device further includes anexpansion member positioned adjacent the movable end portion of the bodywhereby axial movement of the expansion member from the movable endportion toward the fixed end portion results in engagement between theexpansion member and the at least two branch portions to urge the atleast two branch portions apart to expand the body.

In other forms of the present invention, methods are provided for theinsertion of an expandable intervertebral device between an adjacentpair of vertebrae.

One object of the present invention is to provide an expandableintervertebral device that has a reduced size insertion configurationand is expandable from the insertion configuration to a largerconfiguration.

Another object of the present invention is to provide an expandableintervertebral device that has a substantially unobstructed interiorchamber to receive bone growth promoting material.

Still another object of the present invention is to provide anexpandable intervertebral device configured for easy insertion andexpandable to a larger size to establish lordosis.

Yet a further object of the present invention is to provide an improvedmethod for inserting an expandable intervertebral device into a discspace to restore lordosis.

Related objects and advantages of the present invention will be apparentfrom the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an expandable cage according to one embodimentof the present invention.

FIG. 2 a is a side cross-sectional view of the device of FIG. 1.

FIG. 2 b is the device of FIG. 2 a with the inclusion of an expansionwedge according to one embodiment of the present invention.

FIG. 3 is a partial cross-sectional perspective view of the expandablecage of FIG. 1 without an external thread pattern.

FIG. 4 is a perspective view of the expansion wedge of FIG. 2 b.

FIG. 5 is an end view of the expansion wedge of FIG. 4.

FIG. 6 is an elevational view of an insertion tool according to oneembodiment of the present invention.

FIG. 7 a is a sagittal plane view showing a partial cross-sectional sideview of the expandable cage of FIG. 2 b inserted between two adjacentvertebrae in an insertion configuration according to one embodiment ofthe present invention.

FIG. 7 b is the cage of FIG. 7 a shown in an expanded position accordingto one embodiment of the present invention.

FIG. 8 is a top view of an alternative embodiment of the expandable cageof FIG. 1.

FIG. 9 is a side cross-sectional view of the expandable cage of FIG. 8.

FIG. 10 is a partial cross-sectional perspective view of the expandablecage of FIG. 8 without an external thread pattern.

FIG. 11 is a top view of a further embodiment of an expandable cageaccording to the present invention.

FIG. 12 is a side partial cross-sectional view of the expandable cage ofFIG. 11.

FIG. 13 is a partial cross-sectional perspective view of the expandablecage of FIG. 11, without an external thread pattern.

FIG. 14 is a side partial cross-sectional view of a further embodimentof the present invention.

FIG. 15 is a side partial cross-sectional side view of yet a furtherembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated devices, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring now to FIGS. 1 through 3, there is shown a first embodiment ofan expandable cage 10 in accordance with the present invention. In thisembodiment of the invention, expandable cage 10 has a cylindrical outersurface 11 defining an external thread pattern 12 (not shown in FIG. 3)adapted to engage two adjacent vertebra (see FIGS. 7 a and 7 b) and toadvance the cage into the disk space as cage 10 is rotated aboutlongitudinal axis 13. As shown most clearly in FIG. 3, expandable cage10 is substantially hollow with inner surface 21 defining an internalcavity 17. Expandable cage 10 includes a bone in-growth window 16 formedthrough expandable branch 24 and an identical bone in-growth window 19formed through expandable branch 26. These in-growth windows are adaptedto permit communication between the vertebral bodies (FIG. 7) andinternal chamber 17. In most application, bone growth promoting materialwill be placed within internal chamber 17 of expandable cage 10 toencourage bone to grow into and through fusion device 10.

As shown in the accompanying drawings, expandable cage 10 is preferablycomposed of four separate branches, each separated at expandable end 18by a channel extending longitudinally from expandable end 18 towardfixed end 20. Referring now to FIG. 2 a, first expandable branch 24 isseparated from first fixed branch 40 by channel 14. In a similar manner,second expandable branch 26 is separated from first fixed branch 40 bychannel 22. Each of channels 14 and 22 extends from expandable end 18towards fixed end 20. The channels terminate in a slightly largerdiameter radiused opening which preferably acts as a hinge duringexpansion of the device to concentrate stress and deformation adjacentfixed end 20. In a similar fashion, as shown in FIG. 3, second fixedbranch 41 is separated from first expandable branch 24 by channel 15 andfrom second expandable branch 26 by a similar channel (not shown). Thus,expandable cage 10 is formed by four branches, each separated from theother at expandable end 18 by channels extending from outer surface 11to internal chamber 17. The branches are connected at fixed end 20 bylinking area 44 such that each of the branches may move substantiallyindependent from each other at expandable end 18 while remainingconnected to the device by linking area 44. Although the presentembodiment utilizes integrally formed branches, it is contemplated thatseparate components may be joined to form the expandable cage withoutdeviating from the invention.

While four separate branches are shown in a preferred embodiment, it iscontemplated that more or less branches could be utilized withoutdeviating from the spirit or scope of the invention. Moreover, althoughin a preferred embodiment the channels extend from outer surface 11 tointernal chamber 17, it is contemplated that the channels may not extendto the interior chamber. Such a channel may be formed by an overlappinginterface between two adjacent branches without creating an opening forbone in-growth into internal chamber 17. Further, although channels areshown as being preformed in the expandable cage, it is contemplated thatthe channels may be formed as the implant is expanded. By way ofexample, and without limitation, this could occur by rupturing afrangible portion between adjacent branches or by deforming materialdisposed between adjacent branches.

In one aspect of the invention, internal chamber 17 comprises themajority of the volume of the entire cage 10. Specifically referring toFIG. 2 a, external surface 11 defines a diameter 63, excluding threads12. Internal chamber 17 has a diameter of at least 64, that is diameter63 less twice the branch thickness 62.

In a preferred embodiment, branch thickness 62 is selected such that thevolume of internal chamber 17, particularly with the inclusion of voidscreated by in-growth windows 16 and 19 and the various channels,occupies the majority of the entire volume of cage 10. Thus, the presentinvention provides space for a large volume of bone growth promotingmaterial to be inserted into the device to promote bone in-growth.

Adjacent expansion end 18, as shown in FIG. 2 a with respect to branches24, 40 and 26, each of the branches includes inclined surfaces 28, 34and 30, respectively. Adjacent the internal termination of each of theinclined surfaces 28, 34 and 30, is formed an internal shoulder 36, 42and 38, respectively. Referring to FIG. 3, branch 41 includes a similarinclined surface 35 and internal shoulder 43. As shown in FIG. 2 a,arcuate inclined surfaces 28 and 30 are inclined at angle 32 withrespect to each other. In a preferred embodiment, this angle isapproximately 96°, although it is understood that a variety of anglescould be utilized depending on the amount of expansion desired, and thedistance an expansion member will need to travel to create theexpansion.

Referring now to FIG. 2 b, cage 10 is shown with the inclusion ofexpansion wedge 50 disposed adjacent expandable end 18. Expansion wedge50 is further illustrated in FIGS. 4 and 5. Expansion wedge 50 includesfirst and second opposed expansion wedge inclines 52 and 54, which havea tapering arcuate surface that mates with and corresponds to inclinedsurfaces 28 and 30 of branches 24 and 26, respectively. Wedge 50includes side walls 58 and 60 with substantially planar surfaces adaptedto engage inclined surfaces 34 and 35 of fixed branches 40 and 41,respectively. Further, expansion wedge 50 includes a central opening 56which is adapted to receive a driving tool. In a preferred embodiment,central opening 56 is threaded to receive a correspondingly threaded endof a driving tool.

It will be understood that as wedge 50 is advanced toward fixed end 20,inclined surfaces 52 and 54 act upon inclined surfaces 28 and 30,respectively, to urge branches 24 and 26 apart from each other atexpandable end 18. As expansion wedge 50 is inserted along inclinedsurfaces 28 and 30, branches 24 and 26 will tend to expand at expansionend 18 as deformation occurs adjacent fixed end 20. Substantiallycontinuous linking material 44 links all of the branches and does notpermit their expansion at fixed end 20. As wedge 50 is further advancedtoward fixed end 20, the wedge is pushed beyond shoulders 36 and 38,such that wedge 50 is captured within cage 10. As a result of theengagement of back surface 55 of the wedge against shoulders 36 and 38,expansion wedge 50 is prevented from being expelled from the cage, andthe cage is maintained in an expanded condition with the wedge securelyheld in position. It will be understood that the engagement of planarsurfaces 58 and 60 on fixed branches 40 and 41, respectively, tends todeformably expand these branches little, if any, and therefore theyremain substantially fixed in their original positions. Further, fixedbranches 40 and 41 each include shoulders 42 and 43 which engage theback surface 55 of wedge 50 once it has passed beyond the shoulders.Thus, fixed branches 40 and 41 also tend to hold the wedge in place andprevent its expulsion from internal chamber 17.

Referring now to FIGS. 8 through 10, there is shown an alternativeembodiment of the expandable cage of the present invention. In thisembodiment, expandable cage 310 has an outer surface 311 and an externalthread pattern 312 (not shown in FIG. 10). As with the embodiment ofFIG. 1, expandable cage 310 includes two opposed expandable branches 324and 324, and two opposed fixed branches 340 and 341 joined at fixed end320. Each of these branches define inclined surfaces and interiorshoulders adjacent expandable end 318 adapted to engage and receiveexpansion wedge 350. In contrast to the embodiment of FIG. 1, expandablebranch 324 includes two bone in-growth windows 316 and 317, separated byrib 330. In a similar manner, expandable branch 326 includes two bonein-growth windows 322 and 323 separated by rib 332. The use of aplurality of bone in-growth windows in the expandable branches increasesthe overall strength of the branch which may be necessary for longercages or cages constructed of relatively weak materials. While thisembodiment has been shown with two windows per each expandable branch,it is contemplated that more than two bone in-growth windows may beutilized without deviating from the spirit and scope of the invention.

Referring now to FIG. 6, there is shown an insertion tool 70 suitablefor use with an expandable cage according to the present invention.Insertion tool 70 includes an outer sleeve 72 having a drivingprojection 73 adapted to engage driving groove 46 of expandable cage 10.While insertion tool 70 is illustrated with only projection 73, it willbe understood that the device includes an opposing projection (notshown) for mating with a driving groove (not shown) disposed oppositedriving groove 46 on cage 10. Insertion tool 70 further includes handle71 adapted to transmit rotational force to outer sleeve 72 torotationally insert cage 10. Outer sleeve 72 includes an internalchamber, which is occupied by insertion tool inner shaft 75. On thedistal end 77, insertion tool inner shaft 75 includes an externallythreaded area adapted to engage the correspondingly internally threadedcentral opening 56 of expansion member 50. At the proximal end of innershaft 75 there is a handle 76 for providing rotational force to innershaft 75. A series of external threads 78 are formed on inner shaft 75adjacent handle 76. An internally threaded nut 79 is disposed aboutinner shaft 75 and is adapted to engage threads 78 to move inner shaft75 with respect to outer sleeve 72.

In operation, insertion tool 70 is engaged with expandable cage 10 suchas shown in FIG. 7 a. Driving projection 73 of outer tube 72 engagesdriving groove 46 of expandable cage 10 and threaded distal end 77 ofinner shaft 75 threadedly engages threaded opening 56 of expansion wedge50. In this manner, expansion wedge 50 is securely held in positionadjacent the expansion end 18 while the threaded cylindrical cage isinserted into the intervertebral space. In a preferred embodiment, thisdevice is utilized from a posterior approach to the spine with theexpansion wedge 50 being positioned at the leading end of the device.

Referring to FIG. 7 a, expandable cage 10 is threaded intointervertebral space 92 with thread pattern 12 engaging vertebra 80 and82 to advance the cage into the disc space and securely hold it inposition once it has reached a final position as shown in FIG. 7 a.Since the expandable cage is preferably a cylinder having a uniformdiameter, it may be inserted through an insertion tube having a diametersubstantially equal to the thread diameter of the cage 10. As shown inFIG. 7 a, the surface 88 of vertebrae 80 is in contact with outersurface 11 of cage 10. It will be understood that in many applications,a portion of the vertebral end plate will have been removed prior tocage insertion such that cage 10 engages the cancellous bone of thevertebrae. In a similar manner, the surface 90 of vertebrae 82 is incontact with the outer surface 11 of cage 10. In its initial insertionposition, the alignment 84 of vertebrae 80 and the alignment 86 ofvertebrae 82 are in substantial parallel alignment with longitudinalaxis 13 and expandable branches 24 and 26 of cage 10.

Referring now to FIG. 7 b, with threaded end 77 of the insertion devicefirmly engaged in threaded opening 56 of expansion wedge 50 and drivingprojection 73 engaged in driving groove 46, internally threaded nut 79is rotated about external thread 78 to draw shaft 75 within outer tube72 (FIG. 6), thereby advancing expansion wedge 50 toward fixed end 20.As expansion wedge 50 is advanced toward fixed end 20, the inclinedsurfaces of expansion wedge 50 force expandable branches 24 and 26 apartadjacent expandable end 18. In a similar manner, vertebra 80 and 82 areforced apart adjacent expandable end 18 such that the alignment 84 and86 remain substantially parallel to the expandable branches 24 and 26,respectively, and not with longitudinal axis 13 of cage 10. In thismanner, the lordotic curve of the spine may be established andmaintained during the healing process. Moreover, the engagement ofexpansion wedge 50 with the previously described shoulders of each ofthe branches prevents the expansion wedge from being expelled from cage10. The insertion tool may be removed and the substantially unobstructedarea within interior chamber 17 may be filled with bone in-growthmaterial to encourage bone growth through the device. Such bonein-growth material may include autograft, allograft, bone morphogenicproteins in a carrier, or other known bone growth promoting materials.Insertion and expansion of the alternative embodiment shown in FIGS. 8through 10 is accomplished in substantially the same manner.

Referring now to FIGS. 11 through 13, there is shown a furtherembodiment of an expandable cage according to the present invention. Aswith the above-described embodiments of the invention, cage 110 is asubstantially cylindrical device having an outer surface 111 defining anexternal thread pattern 112. Cage 10 defines a substantially cylindricalinternal chamber 117. Cage 110 includes a pair of opposing expandablebranches 152 and 154 separated by a pair of opposing fixed branches 148and 150. Fixed branch 148 is separated from expandable branches 152 and154 by channels 144 and 146, respectively. Fixed branch 150 is separatedfrom expandable branches 154 and 152 by channel 147 and a similarchannel (not shown), respectively. Cage 110 further includes bonein-growth windows 118 and 120 formed through expandable branch 152, andan identical pair of bone in-growth windows 119 and 121 formed throughexpandable branch 154. Each of the bone in-growth windows extend fromouter surface 111 to internal chamber 117. As with the above-describedembodiments, cage 110 includes a large unobstructed internal chamber 117extending along the longitudinal axis 113 from adjacent the expandableend 118 toward the fixed end 114. In the embodiment shown in FIGS. 11through 13, windows 120 and 121 each include a notch 122 and 123adjacent expandable end 118, respectively.

Expander 130 is sized to be received within internal chamber 117.Expander 130 includes a first portion 125 having a projection 126 whichextends into notch 122, and an opposite second portion 127 havingprojection 128 which extends into notch 123. Projections 126 and 128work in conjunction with externally threaded plug 124 in maintaining theposition of expander 130 within cage 110. Expander 130 further includesa bend 132. While a bend may be utilized in the preferred embodiment, itwill be understood that expander 130 may include a fold or a hingebetween portions 125 and 127, that allows adaptation into the reducedsized configuration shown in FIG. 12. First portion 125 includes alongitudinal axis 72 and second portion 127 includes a longitudinal axis70. In the reduced size insertion configuration shown in FIG. 12,longitudinal axis 70 forms an angle 162 with respect to longitudinalaxis 72. In a preferred embodiment, angle 162 is approximately 90°,although other angles are contemplated. In an expanded configuration(not shown), the angle between longitudinal axes 70 and 72 may approach180°, with a 180° angle providing the maximum expansion of the device.

The internal chamber 117 is defined by the four previously describedbranches 148, 150, 152, and 154, each defining a portion of threadpattern 160 (only partially shown in FIG. 12). Plug 124 includes acorresponding external thread adapted to engage thread pattern 160. In apreferred embodiment, a connecting portion 149 extends between fixedbranches 148 and 150 to limit splaying of the fixed branches as threadedplug 124 is advanced toward expandable end 118. Threaded plug 124further includes a central opening 136 adapted to engage an insertiontool extension. In a preferred embodiment, central opening 136 is formedin a hexagonal pattern to accept a similar hexagonally shaped insertiontool (not shown). Cage 110 further includes a driving groove 142adjacent fixed end 114, adapted for engagement with a driving toolprojection to permit insertion of cage 110 between two adjacent bonystructures. The driving tool of FIG. 6 may be utilized with cage 110with the exception that the driving tool inner shaft 75 would include ahexagonally shaped portion at distal end 77. It will be understood thatas threaded plug 124 is threadedly advanced towards expandable end 118,it urges expander 130 into an expanded condition, thereby forcingbranches 152 and 154 apart. As shown in FIG. 13, the expansion mechanismof the present invention provides a large internal cavity to receivebone growth promoting material.

A further embodiment according to the present invention is shown in FIG.14. Cage 180 is fashioned in a similar manner to cage 110 with theexception that it includes a plurality of smaller bone in-growth windowsrather than two large windows in expandable branches 192 and 194.Variations of the number, size, shape and location of bone in-growthwindows as may be dependent on the bone in-growth characteristicsdesired and the material properties of the cage is contemplated by thepresent invention. Further, the mechanism for expansion differs in thatexpander 184 is a substantially planar device, i.e. no bends or hinge,having a longitudinal axis 198. Expander 184 is substantially planar andhas a first end 188 engaged in corner 186 formed between expandablebranch 194 and end wall 199. The opposite end 190 engages and movesalong inner surface 193 of expandable branch 192. Threaded plug 182threadedly engages internal thread pattern 196 formed along the internalsurfaces of the branches. It will be understood that in the unexpandedcondition, axis 198 is skewed with respect to longitudinal axis 197 ofcage 180. However, as threaded plug 182 advances towards expandable end181, expander 184 moves towards an upright position with axis 198 movingtowards a perpendicular arrangement with axis 197. The movement ofexpander 184 towards an upright position expands cage 180. In theexpanded position, there is a large unobstructed internal chamber 189extending from plug 182 to opening 187 adjacent fixed end 195. Thus, thelarge internal chamber 189 may be packed with bone in-growth material topromote fusion between adjacent vertebra.

Referring now to FIG. 15, there is shown still a further embodiment ofthe present invention. Cage 210 includes an outer surface 211 having athread pattern 212 defined thereon. Cage 210 includes a driving groove246 adapted to receive a driving tool such as that previously disclosedherein. Cage 210 further includes a plurality of windows 214communicating from exterior surface 211 to interior chamber 217.Internal chamber 217 is defined by inclined surfaces 216 and 215 (shownin dash), sloping from the expandable end 222 towards the fixed end 224.The slope of inclined surfaces 216 and 215 could also be reversed toallow expansion by movement of the plug 218 in an opposite direction.Plug member 218 includes an external thread pattern adapted to engagewith thread pattern 220 of surfaces 216 and 215. It will be understoodthat as plug member 218 is threadedly advanced toward fixed end 224,branches 230 and 231 are spread apart from one another. As shown in FIG.15, branch 230 includes an area of reduced width 225, adapted to deformas plug member 218 is advanced. As shown, plug member 218 includes acentral opening 237 adapted to receive an insertion tool extension toprovide rotational force. Further, while driving groove 246 is shownformed on expandable end 222, it will be understood that for someinsertion techniques, it will be desirable to have insertion tool groove246 formed on fixed end 224. Moreover, a central aperture may be formedthrough fixed end 224 for passage of an insertion tool extension forengagement with plug 218.

While plugs 124 of the embodiment of FIG. 11, plug 182 of the embodimentof FIG. 14 and plug 218 of the embodiment of FIG. 15 have been shown anddescribed as having a series of external threads for engagement with acorresponding thread pattern defined on the branches of the device, itwill be understood that all the branches, or only the fixed branches ofeach of the devices, may be formed to define a series of ratchets. Witha ratchet configuration, each of the plugs 124, 182, and 218 may bedefined as having an outer surface adapted to advance over the ratchetsto expand the device while having a trailing portion adapted to engagethe ratchets to prevent expulsion. In this manner, the plugs may beadvanced without threading. When utilizing this technique, the insertiontool may be adapted to securely hold the outer cage to prevent itsfurther advancement as a result of the pushing or pulling force exertedon the plug members. In addition to modifications to the plug, the cageitself may be configured for push-in insertion and can be in shapesother than cylinders.

Cages according to the present invention are preferably formed of abiocompatible material having sufficient strength to withstand the loadsthat will be placed upon them for a given application. Additionally, inthe preferred embodiments the material should have sufficientflexibility to undergo at least a small amount of deformation as aresult of the expansion process. Alternatively, for some devices, it maybe desirable to provide hinge points rather than permit the material toundergo a deformation. Most preferably, the material utilized to formthe cages of the present invention is a medical grade titanium alloy.However, the devices could be formed of stainless steel, various typesof plastic, various composites including carbon fiber devices, and boneor bone substitutes.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

1. An expandable interbody device, comprising: a body extendinggenerally along a longitudinal axis between proximal and distal ends andincluding at least two branch portions coupled together adjacent an endportion of said body, each of said branch portions including an outerarcuate surface defining a lateral curvature extending about thelongitudinal axis for engagement with an adjacent vertebra; and anexpansion member positioned between said at least two branch portionswith at least a portion of said expansion member arranged at an angularorientation along said longitudinal axis and with an end portion of saidexpansion member slidably engaged with an inner surface of one of saidbranch portions whereby a change in said angular orientation along saidlongitudinal axis results in sliding displacement of said end portionalong said inner surface to urge said at least two branch portions apartto expand said body.
 2. The device of claim 1, wherein said body has asubstantially cylindrical configuration.
 3. The device of claim 2,wherein said body defines external threads configured for engagementwith vertebral bone.
 4. An expandable interbody device, comprising: abody extending generally along a longitudinal axis between proximal anddistal ends and including at least two branch portions coupled togetheradjacent an end portion of said body, each of said branch portionsincluding an outer arcuate surface defining a lateral curvatureextending about the longitudinal axis for engagement with an adjacentvertebra; and an expansion member positioned between said at least twobranch portions with at least a portion of said expansion memberarranged at an angular orientation along said longitudinal axis wherebya change in said angular orientation along said longitudinal axis urgessaid at least two branch portions apart to expand said body; and whereinaxial displacement of at least a portion of said expansion membergenerally along said longitudinal axis facilitates said change in saidangular orientation of said expansion member.
 5. The device of claim 4,wherein said expansion member includes a first end portion engaged witha first of said branch portions and a second end portion engaged with asecond of said branch portions; and wherein displacement of said firstend portion relative to said second end portion generally along saidlongitudinal axis facilitates said change in said angular orientation ofsaid expansion member to expand said body.
 6. The device of claim 5,further comprising an actuator member positioned between said first andsecond branch portions; and wherein said first end portion of saidexpansion member is positioned adjacent said actuator member and saidsecond end portion of said expansion member is positioned adjacent ashoulder defined by one of said first and second branch portions; andwherein displacement of said actuator member generally along saidlongitudinal axis results in said displacement of said first end portionrelative to said second end portion to facilitate said change in saidangular orientation of said expansion member.
 7. The device of claim 5,wherein said expansion member has a substantially planar configuration.8. The device of claim 4, wherein said at least a portion of saidexpansion member is skewed relative to said longitudinal axis when saidbody is in an initial state; and wherein said at least a portion of saidexpansion member is arranged substantially perpendicular to saidlongitudinal axis when said body is transitioned to an expanded state.9. The device of claim 4, wherein said body defines an internal chamberand a number of bone in-growth openings extending through said body incommunication with said internal chamber.
 10. The device of claim 9,further comprising a bone growth promoting material positioned withinsaid internal chamber to promote bone in-growth through said openingsand into said internal chamber.
 11. The device of claim 9, wherein atleast one of said bone in-growth openings extends through each of saidat least two branch portions in communication with said internalchamber.
 12. The device of claim 4, wherein said body defines a seriesof ratchet elements positioned along said longitudinal axis; and whereina portion of said expansion member is engaged with at least one of saidratchet elements to maintain said expansion member in a select axialposition along said longitudinal axis relative to said body.
 13. Thedevice of claim 12, wherein said portion of said expansion memberdefines an outer surface configured to advance over said ratchetelements and having a trailing portion configured for engagement withsaid at least one of said ratchet elements to maintain said expansionmember in said select axial position.
 14. The device of claim 12,wherein said series of ratchet elements are defined by said at least twoexpandable branch portions.
 15. An expandable interbody device,comprising: a body extending generally along a longitudinal axis andincluding at least two branch portions coupled together adjacent an endportion of said body; and an expansion member positioned between said atleast two branch portions with at least a portion of said expansionmember arranged at an angular orientation relative to said longitudinalaxis whereby a change in said angular orientation relative to saidlongitudinal axis urges said at least two branch portions apart toexpand said body; and an actuator member including an exterior surfaceengaged with inner surfaces of each of said branch portions andpositioned adjacent said expansion member; and wherein displacement ofsaid actuator member generally along said longitudinal axis engaginglyadvances said exterior surface of said actuator member along said innersurfaces of said branch portions which results in said displacement ofsaid at least a portion of said expansion member to facilitate saidchange in said angular orientation.
 16. The device of claim 15, whereinsaid actuator member defines external threads along said exteriorsurface that are engagable along internal threads defined by said innersurfaces of said at least two branch portions to displace said actuatormember generally along said longitudinal axis.
 17. An expandableinterbody device, comprising: a body extending generally along alongitudinal axis between proximal and distal ends and including atleast two branch portions coupled together adjacent an end portion ofsaid body and defining an internal chamber therebetween; and anexpansion member positioned between said at least two branch portionswith at least a portion of said expansion member arranged at an angularorientation along said longitudinal axis whereby a change in saidangular orientation along said longitudinal axis urges said at least twobranch portions apart to expand said body; and wherein said expansionmember includes a first portion and a second portion, said first portionextending along a first axis and engaged with a first of said branchportions, said second portion extending along a second axis and engagedwith a second of said branch portions, said first axis forming an anglerelative to said second axis; and wherein a change in said angle betweensaid first and second axes urges said first and second branch portionsapart to expand said body with said first and second portions of saidexpansion member entirely maintained within said internal chamberbetween said first and second branch portions subsequent to expansion ofsaid body.
 18. The device of claim 17, wherein said first and secondportions of said expansion member are coupled together at aninterconnection location; and wherein axial displacement of saidinterconnection location generally along said longitudinal axisfacilitates said change in said angle between said first and second axesto expand said body.
 19. The device of claim 18, further comprising anactuator member positioned adjacent said interconnection location ofsaid expansion member; and wherein displacement of said actuator membergenerally along said longitudinal axis results in said axialdisplacement of said interconnection location.
 20. The device of claim17, wherein said expansion member includes a hinge interconnecting saidfirst and second portions to facilitate said change in said anglebetween said first and second axes.
 21. The device of claim 17, whereinsaid angle between said first and second axes falls within a range ofabout 90 degrees to about 180 degrees.
 22. The device of claim 17,wherein said expansion member comprises a two-piece element wherein saidfirst portion comprises a first piece and said second portion comprise asecond piece, said first piece including a first end engaged with saidfirst branch portion, said second piece including a second end engagedwith said second branch portion, and wherein said first piece isdirectly connected to said second piece.
 23. An expandable interbodydevice, comprising: a body extending generally along a longitudinal axisbetween proximal and distal ends and including at least two branchportions coupled together adjacent an end portion of said body anddefining an internal chamber therebetween; and an expansion memberpositioned between said at least two branch portions with at least aportion of said expansion member arranged at an angular orientationrelative to said longitudinal axis whereby a change in said angularorientation relative to said longitudinal axis urges said at least twobranch portions apart to expand said body; wherein said expansion memberincludes a first portion and a second portion said first portionextending along a first axis and engaged with a first of said branchportions said second portion extending along a second axis and engagedwith a second of said branch portions said first axis forming an anglerelative to said second axis; and wherein a change in said angle betweensaid first and second axes urges said first and second branch portionsapart to expand said body with said first and second portions of saidexpansion member entirely maintained within said internal chamberbetween said first and second branch portions subsequent to expansion ofsaid body said expansion member including a bend interconnecting saidfirst and second portions to facilitate said change in said anglebetween said first and second axes.